In container molding by the action of a blowing pressure, preforms of thermoplastic material such a preforms of PET (polyethylene terephthalate) are sent through various processing stations within the blow-molding machine. A blow-molding machine of this type typically comprises a heating device for thermally conditioning the preforms and a blowing device, in the area of which the previously tempered preform is expanded by biaxial orientation to form a container. The expansion takes place with the help of compressed air, which is introduced into the preform to be expanded. The sequence of processing steps carried out during this expansion of the preform is explained in DE-OS 43 40 291. The basic configuration of a blow-molding station for forming containers is described in DE-OS 42 12 583. Possible ways of tempering the preforms are explained in DE-OS 23 52 926. Reference is herewith made to the content of these documents.
The blow-molding machine must be supplied continuously with preforms so that the feed to the blow-molding machine will not be interrupted. This is true both for linear blow-molding machines and for those based on the rotary wheel principle. There are two alternative ways in which the preforms can be sent to the blow-molding machine. In the case of the so-called “one-step” method, the preforms are produced by an injection-molding process, and, immediately after they have been injection-molded (and after they have solidified sufficiently), they are transported directly to the blow-molding machine by a conveying apparatus. In the case of the so-called “two-step” method, the preforms are first produced by an injection-molding process and then stored; they are conditioned with respect to their temperature and then blown into containers only at a later time. The production of the preforms and the blow-molding of the preforms into containers can thus take place at different times and at different places.
The two methods have in common that the preforms are sent to the blow-molding machine by a conveying apparatus. Known apparatuses consist of, for example, a vertical conveyor, by which the preforms, which are stored in a collecting bin, are transported to a conveying device. By means of the conveying device, usually a conveyor belt, the preforms are transported to separator device. This separator device has the task of orienting the preforms so that they assume a defined position and of separating them from each other so that they can be transferred properly to, for example, a downstream blow-molding machine. Known separator devices (so-called “roller sorters”) consist of, for example, two conveying rollers, which rotate around their axes in opposite directions and between which a narrow gap remains, which is selected so that the preforms can be held, suspended by their collars, between the rotating conveying rollers. The conveying rollers are arranged with a gradient, that is, at a certain angle to the horizontal, so that the preforms slide along the conveying rollers in the direction of the gradient. In this way, the preforms are sorted in suspended fashion, separated from each other between the rotating rollers, and also conveyed as a result of the gradient.
It is known that it is possible to sort out preforms which have not been properly sorted and which are lying horizontally on, and in alignment with, the conveying rollers instead of being suspended from the conveying rollers. Such sorting-out devices are known from, for example, WO2011/069268 A1. There the sorting-out is realized by the action of a blast of air directed at the misaligned preforms. In this document, additional sorting-out devices according to the prior art are also discussed.
It is also known that rotating wheels can be used to accomplish the sorting-out task; these are also called “kicker wheels”. Kicker wheels are known which are arranged to work in a backflow manner. The rotational axis of such wheels is parallel to, and a certain distance above, the plane defined by the two rotational axes of the conveying rollers of the roller sorter. The rotational direction is selected so that the rotating paddles of the wheel move in the direction opposite to that in which the preforms are being conveyed. A preform which projects above the predefined height is gripped by a paddle of the paddle wheel, pulled out in the direction opposite the conveying direction and opposite the oncoming preforms, and ejected. It is considered a disadvantage that this results in the creation of large gaps in the flow of preforms.
An alternative configuration is described in DE 601 18 772 T2, which shows a kicker wheel arranged above the conveying rollers of a roller sorter. In a first example, the rotational axis of the kicker wheel is parallel to, and a certain distance above, the plane defined by the two rotational axes of the conveying rollers of the roller sorter, wherein the rotational axis is at an angle to its conveying direction. When a preform is gripped, the angled position has the effect of ejecting the preform both to the side and in the backflow direction simultaneously. It is still considered a disadvantage, however, that in this way gaps are formed in the flow of preforms.
In the second example described in DE 601 18 772 T2, the rotational axis of the kicker wheel is parallel to, and a certain distance above, the plane defined by the two rotational axes of the conveying rollers of the roller sorter, wherein the rotational axis is now parallel to the conveying direction. When a preform is gripped, only a sideways-acting ejection force is applied. In this configuration, it is considered disadvantageous that the paddles of the kicker wheel can dip to only a small degree between the conveying rollers and that it is impossible to adjust the height of the wheel.
It is also known from the prior art that the preforms suspended between the conveying rollers can be observed by a sensor system or a camera system, that misaligned preforms can thus be recognized, and that these misaligned preforms can then be ejected by a blast of air and/or by mechanical ejectors.
All of the configurations described above also suffer from the disadvantage that misaligned preforms are sorted out of the flow of preforms, as a result of which the throughput of the preforms can be considerably reduced, especially in the case of high-performance machines.